Tree-shakes side effect free string methods on template literals (#4511)

lukastaegert · web-flow · commit 65068c03d96c · 2022-05-27T10:21:47.000+02:00
diff --git a/src/ast/nodes/Literal.ts b/src/ast/nodes/Literal.ts
@@ -57,10 +57,6 @@ export default class Literal<T extends LiteralValue = LiteralValue> extends Node
 		return path.length > 1;
 	}
 
-	hasEffectsWhenAssignedAtPath(path: ObjectPath): boolean {
-		return path.length > 0;
-	}
-
 	hasEffectsWhenCalledAtPath(
 		path: ObjectPath,
 		callOptions: CallOptions,
diff --git a/src/ast/nodes/TemplateLiteral.ts b/src/ast/nodes/TemplateLiteral.ts
@@ -1,23 +1,59 @@
 import type MagicString from 'magic-string';
 import type { RenderOptions } from '../../utils/renderHelpers';
+import { CallOptions } from '../CallOptions';
+import { HasEffectsContext } from '../ExecutionContext';
 import type { ObjectPath } from '../utils/PathTracker';
+import {
+	getMemberReturnExpressionWhenCalled,
+	hasMemberEffectWhenCalled,
+	literalStringMembers
+} from '../values';
 import type * as NodeType from './NodeType';
 import type TemplateElement from './TemplateElement';
-import { type LiteralValueOrUnknown, UnknownValue } from './shared/Expression';
+import {
+	ExpressionEntity,
+	type LiteralValueOrUnknown,
+	UNKNOWN_EXPRESSION,
+	UnknownValue
+} from './shared/Expression';
 import { type ExpressionNode, NodeBase } from './shared/Node';
 
 export default class TemplateLiteral extends NodeBase {
 	declare expressions: ExpressionNode[];
 	declare quasis: TemplateElement[];
 	declare type: NodeType.tTemplateLiteral;
 
+	deoptimizeThisOnEventAtPath(): void {}
+
 	getLiteralValueAtPath(path: ObjectPath): LiteralValueOrUnknown {
 		if (path.length > 0 || this.quasis.length !== 1) {
 			return UnknownValue;
 		}
 		return this.quasis[0].value.cooked;
 	}
 
+	getReturnExpressionWhenCalledAtPath(path: ObjectPath): ExpressionEntity {
+		if (path.length !== 1) {
+			return UNKNOWN_EXPRESSION;
+		}
+		return getMemberReturnExpressionWhenCalled(literalStringMembers, path[0]);
+	}
+
+	hasEffectsWhenAccessedAtPath(path: ObjectPath): boolean {
+		return path.length > 1;
+	}
+
+	hasEffectsWhenCalledAtPath(
+		path: ObjectPath,
+		callOptions: CallOptions,
+		context: HasEffectsContext
+	): boolean {
+		if (path.length === 1) {
+			return hasMemberEffectWhenCalled(literalStringMembers, path[0], callOptions, context);
+		}
+		return true;
+	}
+
 	render(code: MagicString, options: RenderOptions): void {
 		(code.indentExclusionRanges as [number, number][]).push([this.start, this.end]);
 		super.render(code, options);
diff --git a/src/ast/values.ts b/src/ast/values.ts
@@ -190,7 +190,7 @@ const literalNumberMembers: MemberDescriptions = assembleMemberDescriptions(
 	objectMembers
 );
 
-const literalStringMembers: MemberDescriptions = assembleMemberDescriptions(
+export const literalStringMembers: MemberDescriptions = assembleMemberDescriptions(
 	{
 		anchor: returnsString,
 
diff --git a/test/form/samples/builtin-prototypes/template-literal/_config.js b/test/form/samples/builtin-prototypes/template-literal/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'Tree-shake known string template literal prototype functions'
+};
diff --git a/test/form/samples/builtin-prototypes/template-literal/_expected.js b/test/form/samples/builtin-prototypes/template-literal/_expected.js
@@ -0,0 +1,8 @@
+// deep property access is forbidden
+`ab`.x.y;
+
+// due to strict mode, extension is forbidden
+`ab`.x = 1;
+
+// throws when called
+`ab`();
diff --git a/test/form/samples/builtin-prototypes/template-literal/main.js b/test/form/samples/builtin-prototypes/template-literal/main.js
@@ -0,0 +1,15 @@
+`ab`.trim();
+`ab`.trim().trim();
+`ab`.toString().trim();
+
+// property access is allowed
+const accessString = `ab`.x;
+
+// deep property access is forbidden
+const deepString = `ab`.x.y;
+
+// due to strict mode, extension is forbidden
+`ab`.x = 1;
+
+// throws when called
+`ab`();

Original file line number	Diff line number	Diff line change
`@@ -190,7 +190,7 @@ const literalNumberMembers: MemberDescriptions = assembleMemberDescriptions(`
`190`	`190`	`objectMembers`
`191`	`191`	`);`
`192`	`192`
`193`		`-const literalStringMembers: MemberDescriptions = assembleMemberDescriptions(`
	`193`	`+export const literalStringMembers: MemberDescriptions = assembleMemberDescriptions(`
`194`	`194`	`{`
`195`	`195`	`anchor: returnsString,`
`196`	`196`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+module.exports = {`
	`2`	`+ description: 'Tree-shake known string template literal prototype functions'`
	`3`	`+};`